Internal combustion (IC) engines (e.g. spark-, or compression-, ignition engines) have a plurality of moving parts that require lubrication to prevent damage to the engine. Typically, such engines are provided with a lubrication system comprising a sump (a.k.a. crankcase or oil pan) that collects oil that drains from the moving parts, a plurality of passageways in the engine's block and head for delivering oil to the moving parts, and a pump for pumping oil from the sump through the passageways to the moving parts. A filter is commonly located downstream of the pump to remove unwanted particulates from the circulating oil.
The oil used to lubricate internal combustion engines typically contains one or more perishable, life-extending additives. By “perishable” additive is meant an oil additive that either degrades, evaporates, is consumed or is otherwise lost during operation of the engine, and needs replenishing if the oil is to be effective. By “life-extending” additive is meant an additive that forestalls the degradation of the oil, and maintains its effectiveness for an extended period of time. Additives commonly used with lubricating oils include varying amounts of such things as anti-oxidants (e.g. ca. 0.5%-2.0% by wt. aromatic nitrogen compounds), ashless dispersants (e.g. ca. 2%-10% by wt. polyisobutenyl succinimides), wear retardants (e.g. ca. 0.5-2.0% by wt. zinc dithiophosphates), and detergents (e.g. ca. 2-10% by wt. overbased sulfonates), inter alia. Zinc dithiophosphate (ZDP) also functions as an anti-oxidant. The detergents and dispersants are used to neutralize acids and suspend dirt particles that come mainly from blow-by gases (i.e. gases that pass the rings during combustion). The wear retardants, or anti-wear additives, form a sacrificial, protective film on the metal surfaces to protect the metal from wear. The anti-oxidants prevent oxidation of the oil at normal (i.e. 60° C.-130° C.) oil temperatures, and even more so at high (above 130° C.) oil temperatures such as can occur, for example, when operating the engine under severe conditions (e.g. a car/truck pulling a heavy trailer up a steep grade on a hot day). In this later regard, oil oxidizes more rapidly at temperatures above 130° C., than at normal operating temperatures. With increased oil oxidation, comes an undesirable increase in oil viscosity. The anti-oxidants retard oxidation of the oil, but are consumed in the course thereof, and hence are lost from the oil over time—especially at the higher temperatures where the oil is most susceptible to oxidation. The other additives while less sensitive to temperature, are nonetheless lost from the oil over time, usually as a direct function of engine speed and power.
Engine and vehicle manufacturers recommend that the oil be changed at regular intervals to keep additive levels up. For example, General Motors Corporation, assignee of the present invention, recommends for some of its vehicles that: (1) under normal driving conditions, the oil in its gasoline engines should be changed every seventy five hundred (7,500) miles or 12 months which ever comes first; and (2) under severe operating conditions (e.g. frequent short trips in freezing weather, extended idling, trailer towing, driving in dusty areas, frequent stop & go driving, etc.) the oil should be changed every three months or three thousand (3000) miles. Many vehicle operators forget to change their engine oil regularly, which can be detrimental to the engine. Accordingly, most automobile manufacturers have included oil change warning/reminder systems in their vehicles. One such oil change warning/reminder system is described in U.S. Pat. No. 4,742,476 Schwartz et al. , which is assigned to the Assignee of the present invention, and is intended to be incorporated herein by reference.
Schwartz et al., supra, recognized that excessive degradation of the oil occurs at its temperature extremes. At low oil temperatures (i.e. below about 60° C.), fuel, water and soot tend to accumulate in the oil, reducing its viscosity and increasing wear. At high oil temperatures (i.e. above about 130° C.), the anti-oxidants are depleted, the oil becomes viscous and acidic due to oxidation and nitration, and insoluble particles are deposited on the engine surfaces as varnish or sludge. Acidic oil has a reduced ability to prevent rust and corrosion. Schwartz et al., supra, predicts remaining oil life based on the thermal history of the oil (i.e. time-at-temperature, where time is determined in terms of either engine-revolutions or mileage driven). More specifically, Schwartz et al. uses a computer/controller that determines when an oil change is needed based on empirical data and measured values of oil temperature and engine speed (revolutions per minute) or miles driven. The number of engine revolutions (or mileage driven) corresponding to the maximum engine oil life that would occur if the vehicle were continuously driven under conditions least degrading to the lubricating ability of the oil is stored in a non-volatile memory location in the controller. The oil's thermal history is tracked—that is the temperature of the oil is measured, and the duration the oil is at that temperature as recorded while the engine is in operation. In each period of vehicle operation, the stored number is decremented in accordance with an effective engine-revolutions value determined in relation to the product of measured engine revolutions (or mileage driven) and an engine-oil-temperature-based penalty factor that is determined for each engine and oil. When the oil temperature is in an intermediate, ideal range, the penalty factor is set equal to unity, and the effective engine revolution value accumulates at the measured rate. When the oil temperature is outside the ideal range (e.g. 60° C.-130° C.), the penalty factor is set to a value greater than unity in accordance with a predetermined schedule determined for each engine and oil so that the effective engine revolutions value accumulates at a faster rate than the measured rate. The penalty factor to be applied for each temperature and oil is empirically determined for a particular engine, and generally conforms to a stepped trace similar to that designated as “A” of FIG. 5 hereof. The decremented stored number represents the remaining life of the engine oil which is displayed for the vehicle operator. A visual and/or audible warning indication is given when the stored number is decremented below 10% of its original value, indicating the need for an oil change. Rather than directly measuring the oil temperature, the temperature can be determined indirectly by calculations made from measurements taken on other engine operating conditions (e.g. number of combustion firings, coolant temperature, and engine rotational speed), ala the method discussed in Schwartz et al U.S. Pat. No. 4,847,768, which is intended to be incorporated herein by reference.
Sensors have been proposed for directly measuring the condition (i.e. properties) of the oil. For example, Lee et al. U.S. Pat. No. 5,200,027 discloses an oil degradation sensor that uses two roughened, interdigitated electrodes to directly measure the electrochemical properties of the oil. A saw-toothed voltage is applied to the electrodes to generate an electrochemical current that is measured. The magnitude of the measured current is indicative of the condition of the oil—with lower currents indicating newer/fresher oil and higher currents indicating used/degraded oil. Lee et. Al U.S. Pat. No. 5,200,027 is intended to be incorporated herein by reference. Moreover, Meitzer et al. U.S. Pat. No. 4,733,556 (Mar. 29, 1988) teaches method and apparatus for monitoring changes in the dielectric constant of engine oil as an indicator of its remaining useful life. Meitzer et al. U.S. Pat. No. 4,733,556 is intended to be incorporated herein by reference.
It has been proposed to extend the time period between oil changes by simply adding excess quantities of the additives to the oil to insure that a sufficient amount of additive is present at all times. Moreover, it has been proposed to periodically add the additives to the oil regardless of the oil's usage history. Others have proposed other techniques for adding makeup quantities of additives to the oil. Rohde U.S. Pat. No. 4,066,559 fills an additive-permeable, polyolefin container with the additive, and immerses the container in the oil. At elevated temperatures, the additive diffuses through the wall of the container into the oil. The rate at which the additive diffuses out of the container is reduced as the volume of the additive in the container is reduced, and there is no way provided to replenish the additive in the container when the additive content is depleted. DeJovine U.S. Pat. No. 4,144,166, Lefebvre U.S. Pat. No. 5,591,330 and Lefebvre et al U.S. Pat. No. 5,718,258 provide a soluble composite comprising oil additives embedded in an oil-soluble polymer matrix. Oil passing over the composite (e.g. in an oil filter or other canister) dissolves the matrix polymer, and releases the additives into the oil. The dissolved matrix material contaminates the oil, and retards subsequent dissolution over time. All of these techniques have the prospect of adding too much additive to the oil which has a negative affect on vehicle fuel economy and tailpipe emissions. Accordingly, it is desirable to have controlled addition of the additives so as to keep the additive concentration in the oil within prescribed limits.